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F C Herrera

Publications and source records attributed to F C Herrera.

13 recordsLinked to original sources
PubMed1985

Mechanism of inhibition by lithium of sodium transport in the toad bladder.

Lithium transport across the urinary bladder of Bufo marinus has been studied by means of the short-circuit current technique, as well as unidirectional ion flux measurements. Exposure to lithium of the epithelial (mucosal) surface of this preparation led to a slow, progressive decrease of ion transport, with increasing discrepancy between short-circuit current and lithium influx; in fact there was still an appreciable lithium influx across bladder exposed to amiloride even though short-circuit current was suppressed. Ohmic conductance and sodium efflux barely increased under these circumstances. Upon replacement of lithium by sodium on the epithelial side, the preparations recovered slowly indeed, and residual lithium could be detected in bladder tissue for more than 2 hr while the rate of sodium extrusion at the basal-lateral cell border was slowed down. Recovery from exposure to lithium was accelerated by vasopressin and amphotericin, both of which facilitate sodium entry at the apical border of the epithelium. Thus the lasting deleterious influence of lithium on sodium transport might result from the fact that this ion, once trapped in the cytoplasm, closes the sodium channels.

Amiloride↗
PubMed1982

Irreversible inhibition of epithelial sodium channels by ultraviolet irradiation.

1 The effects of u.v. irradiation at 254 nm and 350 nm on sodium transport across frog skin epithelium have been investigated. 2 Irradiation at 254 nm but not at 350 nm produces a dose-dependent, functionally selective blockade of sodium transport. The effect is apparently due to the irreversible closure of apical sodium channels. 3 The amiloride-sensitive conductance was directly related to sodium transport as measured by short circuit current (SCC) both in normal and irradiated tissues, although both conductance and current were reduced in irradiated tissues. 4 The sensitivity of epithelia to irradiation at 254 nm was defined from the rate constants for the decline in SCC during three 2 min periods of irradiation at 1850 microW cm-2. The rate constant for the initial 2 min irradiation was 0.093 +/- 0.008 min-1. 5 Lowering the sodium concentration to 5.5 mM from 110 mM increased the rate constant to 0.141 +/- 0.014 min-1, consistent with the view that more functional sodium channels exist at lowered sodium concentration. 6 Lowering the temperature to 7 degrees C from 23 degrees C reduced the rate constant to 0.032 +/- 0.007 min-1 suggesting that blockade of channels is not due to a direct interaction with photons. 7 Using a variety of experimental protocols we were unable to demonstrate that bromamiloride or iodoamiloride can act as photoligands for sodium channels in the epithelium of Rana temporaria. This is in contrast to earlier reports with other epithelia.

Amiloride↗
PubMed1980

Increase in epithelial cyclic adenosine 3',5'-monophosphate following vanadate.

Vanadate increases the cyclic adenosine 3',5'-monophosphate (cyclic AMP) content of frog skin epithelium and apparently antagonizes the stimulation by isoprenaline. The effect appears to be a direct activation of adenyl cyclase. This new effect of vanadate together with the inhibitory effects on Na-K ATPase may explain the irregular effects on sodium transport.

Animals↗
PubMed1966

Nonelectrolyte penetration and sodium fluxes through the axolemma of resting and stimulated medium sized axons of the squid Doryteuthis plei.

The penetration of (14)C-labeled erythritol, mannitol, and sucrose through the axolemma was determined in medium sized paired axons, one at rest and the other stimulated 25 times per sec. The resting permeabilities, in 10(-7) cm/sec, are erythritol, 2.9 +/- 0.3 (mean +/- SEM); mannitol, 2.3 +/- 0.4; and sucrose 0.9 +/- 0.1. In the stimulated axons they are: erythritol, 5.2 +/- 0.3; mannitol, 4.0 +/- 0.5; and sucrose, 1.8 +/- 0.3. Thus, the calculated permeabilities during activity (1 msec per impulse), in the same units, are: 100, 75, and 38, respectively. These changes in permeability are reversible. The effects of external potassium and sodium concentrations on erythritol penetration were also studied. At rest, erythritol penetration is independent of potassium and sodium concentrations. In the stimulated axons, erythritol penetration decreases when the extracellular sodium is diminished. Sodium influx (not the efflux) decreases during rest and activity when the extracellular sodium is diminished. The diminution during activity of erythritol and sodium entries in low sodium solutions may be related to a decrease of a drag effect of sodium ions on the nonelectrolyte molecules or to independent effects of the sodium concentration on sodium influx and the nonelectrolyte pathways. The axolemma discriminates among erythritol, mannitol, sucrose, and the different ionic species during rest and activity.

Alcohols↗